1. Field of the invention
The present invention relates to a method of laying out optical fibres across an aperture through the shell of a high pressure container or vessel. The invention is also concerned with a leadthrough system capable of allowing passage of the optical fibres through the shell.
2. Description of the prior art
For the past 20 years, high hydrostatic pressures have increasingly been used in laboratories and in industries for experimental, research and manufacturing works. This has led, in particular, to the development of a new class of high quality measuring sensors using optical fibres and to the development of other high pressure components involving optical fibres and serving to transmit information, gathered by the sensors in and out of the pressure chambers into which the sensors are mounted. However, while such sensors could be employed advantageously for measurements in pressure differentials of up to 200 MPa, this has not been possible due to the lack of reliable leadthrough devices capable of retaining optical fibres, particularly in significant numbers, in the bulkheads or shell of high pressure chambers. This limit in working pressures which is imposed by presently available leadthrough devices, also applies, of course, to high pressure optical investigations such as those relating to the characterizations of solids or liquids under pressure.
A high-pressure, submarine leadthrough device of the above type is disclosed in U.K. patent application G.B. No. 2,058,484 published on Apr. 8, 1981. It is the form of a gland having a tubular strength member that is mechanically secured and sealed to the bulkhead of a vessel or container in which the pressure is held at 15,000 psi (104 MPa). The strength member has a straight bore through which optical fibres or electrical conductors are loosely passed; the bore being thereafter filled with an encapsulating plastics material, such as an epoxy resin, which frictionally adheres to both the fibres of conductors and the bore wall over a length of 150 mm. This device is said to withstand pressure differentials of up to 100 MPa but with such embodiment it seems highly improbable. Indeed, below the critical pressure, the axial load generated by the hydrostatic pressure is wholly transferred to the surrounding wall of the strength member across the encapsulating material. Beyond that pressure however, the resisting frictional force of the plastics material breaks down and the fibres or conductors are blown out of the bore.
Also known are low-pressure devices used in submarine signalling systems involving a fibre-optic cable. They are based on the compression of the cable as it passes through an axial core of a metallic compression block.
A search of the prior art has revealed the following U.S. patent Nos. pertaining to leadthrough devices generally of the relatively low pressure type and acting as supports for optical fibres passing through the bulkhead of a pressure vessel or container:
3,825,320 of 1974--REDFERN PA0 4,217,028 of 1980--REH et al. PA0 4,360,249 of 1982--SLEMON PA0 4,682,846 of 1987--COWEN PA0 3,910,678 of 1975--Mc CARTNEY et al. PA0 4,047,797 of 1977--ARNOLD et al. PA0 4,108,534 of 1978--LOANE et al. PA0 4,610,503 of 1986--MIYAZAKI et al. PA0 4,712,864 of 1987--ELLIS et al. PA0 4,097,129 of 1978--WELLINGTON et al. PA0 4,261,640 of 1981--STANKOS et al. PA0 4,312,563 of 1982--MEAD PA0 4,441,786 of 1984--UHLIN et al. PA0 4,589,727 of 1986--Williams
The following other U.S. patent Nos. are listed here as of general interest only: